Thrust control mechanism

ABSTRACT

A thrust control mechanism for use in association with a combustion engine having a valve means to control the flow of fuel to said combustion engine upon command, which is responsive to a pressure responsive member for sensing thrust as a function of the pressure drop across said combustion engine exhaust nozzle. Said thrust control mechanism may further include an absolute reference means to compensate for changes in ambient pressure of the device and a variable nozzle area input means to compensate for changes in combustion engine thrust due to different settings of nozzle area.

United States Patent [56] ReterencesCited 4 UNITED STATES PATENTS2,683,349 7/1954 Lawrence Primary Examiner-Al Lawrence SmithAttorney-Plante, Arens, Ham and OBrien ABSTRACT: A thrust controlmechanism for use in association with a combustion engine having a valvemeans to control the flow of fuel to said combustion engine uponcommand, which is responsive .to a pressure responsive. member forsensing thrust as a function of the pressure drop across said combustionengine exhaust nozzle. Said thrust control mechanism may further includean absolute reference means to compensate for changes in ambientpressure of the device and a variable nozzle area input means tocompensate for changes in combustion engine thrust due to differentsettings of nozzle area.

[72] Inventor Samuel E. Arnett South Bend, Ind. [2]] Appl. No. 748,416[22) Filed July 29, i968 [45] Patented Mar. 23, 1971 [73] Assignee TheBendix Corporation [54]- THRUS T CONTRQL MECHANISM 7 Claims, 4'Drawiug1igs. 52 use: 60/243,

. 60/39. 28 [51] Int. Cl F02k 3/00, F020 9/08 [50] Field of Search60/237, n 235, 243, 39.28

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so @25 a! 56' p 45 i r 36 r a 55 J 4 ea 76 7 52 4 17 74154 n 42 PATENTEUM2319?! SHEET 2 BF 2 FIE INVENTO R. SAMUELE. AIENETT BY ATTORNEYSBackground of the Invention This invention relates, in general, tocombustion engine fuel controls and, in particular, a thrust controlmechanism to override upon command a conventional fuel control conceptfor a gas turbine engine.

The conventional gas turbine engine fuel control systems with which I amfamiliar employ concepts and structure that maintain engine speed at aselected value. Thus, for example, as a vertical takeoff and landingaircraft approaches a landing surface, hot exhaust gases are deflectedoff the landing surface and recirculate to the gas turbine engine inlet.This increases the inlet temperature and engine speed starts to increasebeyond the selected value. To decrease speed, the fuel flow to theengine is then automatically reduced with a resulting decrease inthrust. This sequence of events could result in a serious aircraftattitude problem and an unstable uncontrolled landing. Further, someaircraft experience during supersonic flight, a power setting of enginespeed or afterbumer fuel-toair ratio which result in an unstableintersection of thrust and drag. Still further, specific selection ofspeeds on a multiengine aircraft does not generally result in optimizedindividual engine performance in terms of fuel consumption.

Summary of the Invention It is the purpose of this invention to providea thrust control mechanism whereby engine performance may be controlledas a function of thrust measured across said gas turbine engine exhaustnozzle. With regard to vertical takeoff and landing, if thrust in lieuof engine speed were being controlled, the engine cgntrol would changeonly enough to compensate for changes in specific fuel consumption. Thatis to say, since thrust is equal to the fuel flow divided by specificfuel consumption, the only change that it is required is to compensatefor the change in specifics. This change is small in magnitude andoccurs smoothly resulting in improved landing control.

It is another object of this invention such that at the unstableintersection of thrust and drag that can exist in supersonic flight,thrust control of the gas turbine engine may be selected and,automatically, a stable thrust-drag intersection would result.

It is another object of this invention to provide individual thrustcontrol of the various engines so that the thrust may be varied alongwith aircraft trim to obtain optimum gas turbine engine fuelconsumption.

Otherobjects and features of the invention will be apparent from thefollowing description of the thrust control mechanism taken inconnection with the accompanying drawings.

Brief Description of the Drawings FIG. 1 is a sectional schematic of thecomponents comprising the thrust control mechanism shown in associationwith a gas turbine engine and its conventional fuel control;

FIG. 2 is a modified sectional schematic of the components comprisingthe thrust control mechanism shown in FIG. 1 but excluding the resilientmeans for providing rate of change of fuel flow information.

FIG. 3 is a modified sectional schematic of the components comprisingthe thrust control mechanism shown in FIG. 2 including an absolutereference means; and

FIG. 4 is a modified sectional schematic of the components comprisingthe thrust control mechanism shown in FIG. 3 including a variable nozzlearea input means.

Description of the Preferred Embodiment Referring now to the drawingsand particularly to FIG. 1, numeral designates a gas turbine enginehaving a casing 12 with an air inlet 14 and an outlet or exhaust nozzle16. Air from the inlet 14 flows through a compressor 18 driven by aturbine or turbines 20 via a shaft 22 suitable mounted for rotation incasing 12. The pressurized air at pressure P. discharged from compressor18 flows to combustion chambers 24 where pressurized fuel injected byfuel nozzles 26 is mixed with the air and burned to provide a flow ofhot motive gas. The hot motive gas flows through turbine 20 driving thesame and exhausts therefrom to the nozzle 16 from which the gas exits tothe atmosphere to provide propelling thrust.

The fuel nozzles 26 are connected to a fuel manifold 28 which receives apressurized metered flow of fuel via a fuel conduit 30 leading from theoutlet 32 of a fuel control 34. A supply fuel conduit 36 connects a fueltank 38 with inlet 40 of fuel control 34. An engine driven fuel pump 42connected to conduit 36 serves to pressurize the fuel passing to inlet40.

The fuel control 34 is provided with a casing 44 having inlet and outletports, 40 and 32, respectively, formed therein. Fuel flow from the inlet40 to the outlet 32 is controlled by a valve means comprising a variablearea metering orifice 46 and a metering or control valve 48 whichcooperates with the orifice 46 to establish an effective flow area, andthus, rate of fuel flow to the combustion chamber 24. A constantpredetermined fuel pressure drop 'P,P across orifice 46, is maintainedby a conventional bypass valve mechanism generally indicated by 50 whichis responsive to the pressure drop PlP across orifice 46 and whichfunctions to divert more or less fuel at pressure P depending upon therelative pressure drop error across orifice 46 from the upstream side oforifice 46 back to the inlet of fuel pump 42 at relatively low pressureP to thereby cause a decrease or increase in the pressure as required tomaintain the constant predetermined drop P,P A drain passage 52 ventsthe interior of casing 44 to passage 36 at fuel pump inlet pressure P,,.

The metering valve 48 is operatively connected to and actuated by aservo piston 54 slidably carried in casing 44 and separating chambers 56and 58 which are pressurized by fuel controlled by a servo flapper valve60 in cooperation with orifice 62 which receives fuel pressure P;through a restriction 64 from fuel pressure P,. Chamber 56 receives saidfuel pressure P;, through passage 65 as a function of the position offlapper valve 60 relative to orifice 62. The-servo piston 54 isoperatively connected to a fuel scheduling cam 66, suitable guided onone end by the casing 44 and slidably retained in a cavity 68 of thecasing 44 on its other end, by means of a spring retainer 70 operativelyattached to said servo piston 54, a spring 72, a double-ended springretainer 74, a spring 76 and a spring retainer 77 slidingly retained bycasing 44. Servo flapper valve 60 is pivotally retained by casing 44 viapin 78 and pivotally attached intermediate said double-ended springretainer by pin 80. The fuel scheduling cam 66 may be operativelyconnected to reflect numerous parameters as variable functions of engineperformance or pilot initiated commands to the engine. The spring 76serves to convert the position setting of the fuel scheduling cam 66into a force acting upon the servoflapper valve 60 and the spring 72reacts against its retainer 70, being opposed to movement by fuelpressure P to provide a force-opposing feedback which nulls the forcetransmitted to the servo flapper valve 60 by the spring 76. Theservoflapper valve 60 is responsive to the fuel scheduling cam 66 so asto control the effective area of orifice 62 and thus regulate the servopressure P in chamber 56 to position servo piston 54.

The servoflapper valve 60 in cooperation with orifice 62 derive adownstream pressure I that may be made available at an outlet 61 tofacilitate further control of the fuel control 34 by a complementingengine control system. Further, an inlet 63 is provided in the casing 44to vent returning fuel from the complementing engine control system topressure P,,. As may be seen by those skilled in the art, the fuelcontrol 34 and the complementing engine control may be combined into asingle structure should it be desirable for a specific application. If acomplementing engine control is not used, the outlet 61 may merely bevented to pressure P, through inlet 63 to make an operable system.Chamber 58 has a pressure I that will vary in proportion to the rate ofchange of the position of the servopiston 54. Pressure P may be madeavailable at outlet 82 to provide a lead function to a complementingengine control system. Pressure P is vented through a restriction 84 tofuel pressure 1%. Thus, during any period when the servo piston 54 isnot changing position, pressure P will equal P and a lead functionsignal will not be reflected by pressure P at outlet 82. If acomplementing engine control system is not used the outlet 82 may merelybe closed off to prevent fuel leakage to the outside ambient.

A thrust control mechanism 86 complements the fuel control 34 forcontrol of the gas turbine engine 10. The thrust control mechanism 86,as shown in FIG. 1, has a casing 88 wherein a diaphragm 90 defineschambers 92 and 94. Chamber 92 receives total nozzle pressure P throughinlet 96, passage 98 and pressure sensing element 100, immediatelyupstream from the gas turbine exhaust nozzle 16. The diaphragm 90 isresponsive on one side to variations in nozzle pressure P,. Diaphragm 90is responsive to its other side to ambient air pressure P, enteringchamber 94 through inlet 102 and has rigidly attached thereto a shaft103 and a spring retainer 104. A second shaft 105 and spring retainer106 are slidingly retained by casing 88. A spring 107 is retainedbetween the spring retainers 104 and 106 and therewith comprises athrust request means which translates thrust position information into aforce to act upon a valve or lever means 108. The diaphragm 90 isresponsive to the thrust of the gas turbine engine and acts in aforce-opposing relationship with the thrust request means to null anyrequested increase or decrease in thrust. The lever means 108 ispivotally attached to the casing 88 by pin 110 and has its one endpivotally attached to the shaft 103 by pin 112 while its other endextends into chamber 114 and defines a valve 116. Chamber 114 receivesfuel pressure P from outlet 61 through passage 117, inlet 118 and anorifice 120 and vents through outlet 122, passage 124 and inlet 63 tofuel pressure P A bellows 126, responsive through passage 128 and inlet130 to servo piston rate of change pressure P is rigidly fixed on oneend to casing 88 and pivotally attached by pin 132 to lever means 108.The bellows 126 relates to the lever means 108, an anticipatory force asa function of the rate of change of the servo piston 54 and thecorresponding fuel flow to the gas turbine engine 10 to damp theresponse of the lever means 108 to the request for thrust means. Upon arequest for thrust the valve 116 in cooperation with orifice 120controls the pressure P, and can thereby override the normal control ofthe fuel control 34 by the fuel scheduling cam 66 to decrease the fuelflow rate established by fuel scheduling cam 66. It is noted that thethrust control mechanism 86 may never override the fuel scheduling cam66 to increase the fuel flow rate established by the fuel scheduling cam66. When the thrust control mechanism 86 overrides the otherwise normalfunctioning of the fuel control 34, fuel flow to the gas turbine engine10 will vary directly as a function of a specific request for thrust. Itis noted that the shaft 105, responsive to a request for thrust, may beoperatively attached to a manual control system available to theoperator of the gas turbine engine 10 or preprogrammable by structuresimilar to fuel scheduling a cam 66 or equivalent.

As can be seen by those skilled in the art the fuel control 34 andthrust control mechanism 86 casings can be made of two or more parts toenable assembly of the various components therein. Although notpreviously mentioned, those skilled in the art will further see thatseals may be employed in the appropriate placed to preclude fuelleakage.

Mode of Operation of the Preferred Embodiment Initially, it will beassumed that the gas turbine engine 10 is stable in operation with thefuel scheduling cam 66 set to provide a near maximum fuel flow. Thus,the flapper valve 60 is open relative to orifice 62. Further, it isassumed that a reasonably low value of thrust has been selected, andthus, the flapper valve 116 is only partially opened with respect toorifice 120. The system as a whole is in a null condition.

The shaft is moved in the direction of the arrow shown in FIG. 1, torequest increased thrust from the gas turbine engine 10. Spring 107 willcompress and convert a position input from shaft 105 and spring retainer106 into a force, causing spring retainer 104 and shaft 103 to actagainst the diaphragm 90 and nozzle pressure P such that lever means 108is pivoted about pin to further open valve 116 relative to orifice 120.Thus, pressures P and P drop, since valve 60 is open with respect toorifice 62. The drop in pressure P allows servopiston 54 to move to theleft in response to pressure P acting against valve 48. As servopiston54 and valve 48 move to the left, increased fuel flow is provided to thegas turbine engine which upon combustion results in increased thrustvent ing through exhaust nozzle 16. The increase in thrust has a finiteresponse time which is a function of the flow rates of the system, andthus, increased thrust is not instantaneously available upon a requestfor increased thrust. The increasing thrust will be sensed by element100 and communicated through passage 98 and inlet 96 to chamber 92 toact upon discharge diaphragm 90 in opposition to the request forincreased thrust. The increased nozzle pressure P will, acting alone ondiaphragm 90, eventually null the thrust control mechanism 86 and thusthe fuel control 34. However, as servopiston 54 moves to the left inresponse to a request for increased thrust, spring retainer 70compresses spring 72 so as to exert a first force on flapper valve 60 tofurther close it relative to orifice 62. This first force is opposed bya second force resulting from spring retainer 74 tending to compressspring 76 against spring retainer 77. The second force tends to damp thefirst force with respect to further closing flapper valve 60 andbringing the system to a null. To further refine the responsiveness ofthe system, a thrust request lead signal may be provided to anticipatethe conditions necessary for a null as soon as possible after a thrustrequest has been made. The fuel control 34 derives such a lead signal atoutlet 82 as servopiston 54 moves to the left in response to a requestfor increased thrust. The existing pressure P in chamber 58 will beequal to pressure P however, as piston 54 moves to the left the volumeof chamber 58 will increase and the pressure P will drop below pressureP, since restriction 84 will preclude instantaneous flow of P intochamber 58. The actual pressure level of pressure P,; will vary as afunction of the rate of change of position of servopiston 54. Thus, thefaster the rate of change of position of piston 54 the greater thepressure difference between P and P since a slow rate of change wouldallow P to flow through restriction 84 into chamber 58 so as to precludea pressure difference. The P pressure drop developed in chamber 58 willbe communicated via outlet 82, passage 128 and inlet 130 to bellows 126.The bellows 126 will retract tending to cause lever means 108 to furtherclose valve 116 relative to orifice 120. This lead signal isfunctionally intended to dampen and smooth the responsiveness of thethrust control mechanism 86 to the increasing nozzle pressure P, as itis imposed upon the diaphragm 90, and thus lever means 108 to closevalve 116 relative to orifice in bringing the thrust control mechanismagain to a null condition. As valve 116 approaches a null condition withrespect to orifice 120, pressures P and P will increase. When pressureP, increases, it will cause the servopiston to approach a null conditionrelative to pressure P acting on valve 48. Thus, when the thrust controlmechanism 86 nulls, the fuel control 34 will correspondingly null.

It is understood that a request to the thrust control mechanism todecrease thrust will result in an identical converse action.

DESCRIPTION OF THE MODIFIED EMBODIMENTS In the embodiments shown inFIGS. 2, 3 and 4, those parts which are identical to corresponding partsof the preferred embodiment, depicted in FIG. 1, will be given the sameidentifying numbers.

The thrust control mechanism shown in FIGS. 2, 3 and 4, are intended tofunction in cooperation with the fuel control 34 shown in FIG. 1 forcontrol of the gas turbine engine 10.

It is parenthetically mentioned that the thrust control mechanism 86shown in FIG. 1 need not contain the bellows 126 to provide thrustcontrol override of the fuel control 34. The bellows 126 enables thrustcontrol refinement in that it provides an input to the thrust controlmechanism to allow it to more smoothly achieve a null condition inresponse to a request for a change in thrust. Thus, FIG. 2 depicts asectional schematic of the components comprising the thrust controlmechanism shown in FIG. 1, but excluding the bellows 126 to depict asimplified form of the invention.

FIG. 3 is a modified sectional schematic of the components comprisingthe thrust control'mechanism shown in FIG. 1 including n absolutereference means 140. The absolute reference means 140 is comprised of anevacuated bellows 142 being rigidly mounted to casing 88 on one end andfree on its other end to vary as a function of ambient pressure changes,a shaft 144 pivotally attached by a pin 146 to the bellows 142,and aroller means 148 pivotally attached by a pin 150 to the shaft 144. Theroller means 148 is operatively positioned intermediate the lever means108 and the spring retainer 104 to transmit a request for thrust forcefrom said spring retainer 104 to said lever means 108. The position ofthe roller means 148 is a function of bellows 142 expansion orcontraction in response to a decreased or increased ambient pressure PThus, as the roller means 148 changes position, the lever am! of thethrust requestforce is changed to compensate for variations in ambientpressure P FIG. 4 is a modified sectional schematic of the componentscomprising the thrust control mechanism shown in FIG. 3 including avariable nozzle area input means 152. The variable nozzle area inputmeans 152 is comprised of a lever 154 pivotally attached to casing 88 bya pin 156, a shaft 158 slidingly projecting outside the casing 88through an opening 159, and a roller means 160 pivotally attached by apin 162 to the shaft 158. The lever 154 operatively engages the rollermeans 160. The roller means 160 and the lever 154 are operativelypositioned intermediate the lever means 108 and the roller means 148 totransmit a request for thrust force from said spring retainer 104 androller means 148 to said lever means 108. The position of the rollermeans 160 is a function of the response of shaft 158 to a change inengine exhaust 16 nozzle area through a linkage (not shown) from the gasturbine engine to the thrust control mechanism 86. Thus, as the rollermeans 160 changes position, the lever arm of the thrust request force ischanged to compensate for changes in engine exhaust nozzle 16 area.

MODE OF OPERATION OF MODIFIED EMBODIMENTS With reference to FIG. 3, thethrust control mechanism 86 is provided an absolute reference means 140to compensate for ambient pressure P, changes experienced whileoperating the gas turbine engine 10 at varying altitudes. It is assumedthat the gas turbine engine 10, the fuel control 34, and the thrustcontrol mechanism 86 are mounted on an aircraft, not shown. As theaircraft climbs in altitudethe ambient pressure P,, decreases, and agreater value of P,P,, is necessary to maintain the predetermined thrustrequest. Bellows 142 will expand and position the roller means 148 tothe left to give the request for thrust force a larger lever arm withrespect to lever means 108 thus requiring an increase in P,-P,, to nullthe system.

It is noted that an absolute reference means may or may not be adesirable compensation for the thrust control mechanism depending uponthe responsiveness of the control to sensing errors resulting fromaltitude changes.

It is understood that a decrease in altitude causing an increase inambient pressure P will result in an identical converse action.

With reference to FIG. 4, the'thrust control mechanism 86 is furtherprovided a variable nozzle area input means 152 to compensate forchanges in engine thrust as a function of the area of the exhaust nozzleof gas turbine engine 10. It is assumed that the gas turbine engine 10,the fuel control 34 and the thrust control mechanism 86 are mounted onan aircraft, (not shown) and that the engine is being operated undernormal conditions. If the operator of the aircraft makes a changethrough a conventional nozzle area varying mechanism, (not shown), toreduce the area of engine exhaust nozzle 16, a change in P P,, must berequested to maintain the same predetermined thrust as set by shaft 105.As nozzle area reduces the linkage responsive to engine exhaust nozzle16 area and operatively attached to shaft 158 will position the rollermeans 160 to the left to give the request for thrust force a largerlever arm with respect to lever means 108, thus P,-P,, must increase toexert a nulling force on the lever means 108 due to the decreasingchange in nozzle 16 area.

It is understood that a change in controls to increase the area ofengine exhaust nozzle 16 will result in an identical converse action.

While the specific details have been herein shown and described, theinvention is not confined thereto, as other substitutions can be madewithin the spirit and scope of the invention.

I claim:

1. A thrust control mechanism for use with a combustion engine equippedwith an exhaust nozzle, said control mechanism comprising:

first valve means operatively connected to control fuel flow to saidcombustion engine;

a means responsive to a request for increased or decreased thrust; 7

said first valve means being responsive to said means responsive to arequest for increased or decreased thrust to accordingly increase ordecrease, respectively, the fuel flow to said combustion engine andthereby increase or decrease engine thrust;

a pressure responsive member receiving exhaust nozzle pressure on oneside and ambient pressure on its other side for sensing thrust as afunction of the pressure drop across said exhaust nozzle;

said first valve means being responsive to said pressure responsivemember;

said pressure responsive member being in a force opposing relationshipwith said means responsive to a request for thrust and responsive to achange in engine thrust to move said first valve means to null saidthrust control mechanism;

a resilient means defining a fluid filled variable volume chamberoperatively connected to receive a fluid pressure variable as a functionof the rate of change of fuel flow to said combustion engine; and

said resilient means being operatively connected to said first valvemeans to oppose said request for increased or decreased thrust as afunction of said rate of change of fuel flow.

2. A thrust control mechanism for use with a combustion engine asrecited in claim 1 and further including:

a source of pressurized fuel;

a fuel conduit connected to deliver fuel from said source to saidcombustion engine;

a variable area fuel control valve means operatively connected to saidfuel conduit for controlling fuel flow therethrough;

a bypass valve means across said fuel control valve means formaintaining a predetermined constant pressure drop thereacross;

a fuel schedule means to vary the setting of said fuel control valvemeans through a servo means in response to predetermined variableinputs; and

said first valve means operatively connected to said servo means tooverride the control of said fuel control valve means by said fuelschedule means.

3. A thrust control mechanism for use with a combustion engine asrecited in claim 1 and further including:

a source of pressurized fuel;

a fuel conduit connected to deliver fuel from said source to saidcombustion engine;

a fuel control valve means operatively connected to said fuel conduitfor controlling fuel flow therethrough;

a bypass valve means operatively connected to said fuel conduit forcontrolling the pressure drop across said fuel control valve means;

a fuel schedule means to vary the setting of said fuel control valvemeans in response to predetermined variable inputs; and

said first valve means operatively connected to said fuel control valvemeans to override the control thereof.

4. A thrust control mechanism for use with a combustion engine asrecited in claim 1 and further including:

a source of pressurized fuel;

a fuel conduit connected to deliver fuel from said source to saidcombustion engine;

a fuel control valve means operatively connected to said fuel conduitfor controlling fuel flow therethrough;

a fuel schedule means to vary the setting of said fuel control valvemeans through a servo means in response to predetermined variableinputs; and

said first valve means operatively connected to said servo means tooverride the control of said fuel control valve means by said fuelschedule means.

5. A thrust control mechanism for use with a combustion engine asrecited in claim 1 and further including:

a source of pressurized fuel;

a fuel conduit connected to deliver fuel from said source to saidcombustion engine;

a fuel control valve means operatively connected to said fuel conduitfor controlling fuel flow therethrough;

a fuel schedule means including cam means to vary the setting of saidfuel control valve means in response to predetermined variable inputs;

said first valve means operatively connected to said fuel control valvemeans to override the control thereof.

6. A thrust control mechanism for use with a combustion engine asrecited in claim I wherein said first valve means comprises:

a lever having a flapper valve on one end to control said fiow of fuelto said combustion engine;

said lever being pivotally attached to rigid structure intermediate itsends;

said lever being pivotally responsive, near its other end. to

said pressure responsive member;

said lever being further responsive, near its other end, to said meansresponsive to a request for increased or decreased thrust.

7. A thrust control for use with a combustion engine as recited in claim1 wherein said means responsive to a request for increased or decreasedthrust is a spring means of predetermined compressibility.

1. A thrust control mechanism for use with a combustion engine equippedwith an exhaust nozzle, said control mechanism comprising: first valvemeans operatively connected to control fuel flow to said combustionengine; a means responsive to a request for increased or decreasedthrust; said first valve means being responsive to said means responsiveto a request for increased or decreased thrust to accordingly increaseor decrease, respectively, the fuel flow to said combustion engine andthereby increase or decrease engine thrust; a pressure responsive memberreceiving exhaust nozzle pressure on one side and ambient pressure onits other side fOr sensing thrust as a function of the pressure dropacross said exhaust nozzle; said first valve means being responsive tosaid pressure responsive member; said pressure responsive member beingin a force opposing relationship with said means responsive to a requestfor thrust and responsive to a change in engine thrust to move saidfirst valve means to null said thrust control mechanism; a resilientmeans defining a fluid filled variable volume chamber operativelyconnected to receive a fluid pressure variable as a function of the rateof change of fuel flow to said combustion engine; and said resilientmeans being operatively connected to said first valve means to opposesaid request for increased or decreased thrust as a function of saidrate of change of fuel flow.
 2. A thrust control mechanism for use witha combustion engine as recited in claim 1 and further including: asource of pressurized fuel; a fuel conduit connected to deliver fuelfrom said source to said combustion engine; a variable area fuel controlvalve means operatively connected to said fuel conduit for controllingfuel flow therethrough; a bypass valve means across said fuel controlvalve means for maintaining a predetermined constant pressure dropthereacross; a fuel schedule means to vary the setting of said fuelcontrol valve means through a servo means in response to predeterminedvariable inputs; and said first valve means operatively connected tosaid servo means to override the control of said fuel control valvemeans by said fuel schedule means.
 3. A thrust control mechanism for usewith a combustion engine as recited in claim 1 and further including: asource of pressurized fuel; a fuel conduit connected to deliver fuelfrom said source to said combustion engine; a fuel control valve meansoperatively connected to said fuel conduit for controlling fuel flowtherethrough; a bypass valve means operatively connected to said fuelconduit for controlling the pressure drop across said fuel control valvemeans; a fuel schedule means to vary the setting of said fuel controlvalve means in response to predetermined variable inputs; and said firstvalve means operatively connected to said fuel control valve means tooverride the control thereof.
 4. A thrust control mechanism for use witha combustion engine as recited in claim 1 and further including: asource of pressurized fuel; a fuel conduit connected to deliver fuelfrom said source to said combustion engine; a fuel control valve meansoperatively connected to said fuel conduit for controlling fuel flowtherethrough; a fuel schedule means to vary the setting of said fuelcontrol valve means through a servo means in response to predeterminedvariable inputs; and said first valve means operatively connected tosaid servo means to override the control of said fuel control valvemeans by said fuel schedule means.
 5. A thrust control mechanism for usewith a combustion engine as recited in claim 1 and further including: asource of pressurized fuel; a fuel conduit connected to deliver fuelfrom said source to said combustion engine; a fuel control valve meansoperatively connected to said fuel conduit for controlling fuel flowtherethrough; a fuel schedule means including cam means to vary thesetting of said fuel control valve means in response to predeterminedvariable inputs; said first valve means operatively connected to saidfuel control valve means to override the control thereof.
 6. A thrustcontrol mechanism for use with a combustion engine as recited in claim 1wherein said first valve means comprises: a lever having a flapper valveon one end to control said flow of fuel to said combustion engine; saidlever being pivotally attached to rigid structure intermediate its ends;said lever being pivotally responsive, near its other end, to saidpressure responsive member; said lever beIng further responsive, nearits other end, to said means responsive to a request for increased ordecreased thrust.
 7. A thrust control for use with a combustion engineas recited in claim 1 wherein said means responsive to a request forincreased or decreased thrust is a spring means of predeterminedcompressibility.